EVALUATING ALTERNATIVES FOR DISPOSING OF WATER PLANT SOLIDS INTO A WASTEWATER PLANT Matthew Valade, P.E. July 25, 2014 Barboe.pptx
Presentation Outline Project Background Why Dewater Croton Residuals Offsite? Pilot Study at Hunts Point WWTP Final Resolution Conclusions
New York Water Supply: Tunnels and Aqueducts 3
Croton WTP - A Brief History 1842 Croton begins supplying water to NYC 1997 Consent Order required Croton filtration 1999 Mosholu Golf Course (Bronx) site selected 2001 Design stopped due to legal clarification of use of public park land this design included residuals dewatering facilities on site 2002-04 Several sites evaluated MGC again selected but smaller footprint required Design does not include on site residuals dewatering 2005 Construction work for Croton WTP begins 2014 Startup is underway
Treatment Process Sodium hypochlorite (intermittent) Mixer 1 Mixer 2 Coagulant Polymer Mixer 3 Filter Aid Polymer Flocculation Sodium hypochlorite Solids Dissolved Air Flotation Fluoride Corrosion inhibitor Sulfuric Acid ph Balance Coagulant Backwash Filtration Waste Washwater UV Sodium hydroxide Sodium hypochlorite
Overview of the Facility Location Jerome Park Reservoir Plant Site Mosholu Golf Course Woodlawn Train Station Jerome Avenue Woodlawn Cemetery Photograph taken in 2004 before construction
Croton Water Treatment Plant
Final Excavation - July 6, 2007 N 555-ft 90-ft Treated Water Tunnel 683-ft Raw Water Tunnel 9.2 Acres
Construction as of May 2010
Construction as of May 2014
Why Dispose Croton Residuals Offsite? Dewatering residuals on-site: Limited space on site No truck access to Operating Level below grade Concerns with truck exhaust Space Constraints Reduce truck traffic to and from the WTP Considerably higher Cap/Op costs Issues with dewatering Croton residuals on-site led DEP to consider dewatering residuals offsite at Hunts Point WWTP
Why Hunts Point? Discharging Directly to Sewer was Banned Closest WWTP to site Existing Dewatering Facility Sufficient space for any required facilities Sufficient Dewatering capacity 13 dewatering centrifuges Space for 3 new centrifuges 7.5 mile Force Main Required Croton WTP Hunts Point WWTP
Croton WTP Flow and Residuals Solids Loads Croton WTP Flow, MGD Total Suspended Solids, lb/day Average Design Conditions Maximum Design Conditions 144 17,300 290 44,500
Characteristics of Croton WTP Residuals WTP Residuals Dissolved Solids Parameter Concentration TSS 30 mg/l Aluminum 1,700 mg/l Iron 150 mg/l Manganese 55 mg/l Heavy Metals Trace Amount Toxic Or hazardous None ph ~ 6.2 units Aluminum Hydroxide 50% Organic 41% Other inert (metals, non-organic solids) 9%
Hunts Point WWTP Background Biosolids loads Hunts Point WWTP: 100,000 lb/day Imported Sludge: 214,000 lb/day Dewaters thickened, digested biosolids Hunts Point and imported biosolids from other NYCDEP WWTPs separately Pelletize dewatered biosolids prior to off site disposal
Croton Residuals Dewatering Alternatives at Hunts Point Separate Dewatering Dewater water treatment residuals and wastewater biosolids sludge separately Blend Croton residuals with Hunts Point sludge Introduce at primary/secondary settling and dewater water treatment residuals and wastewater biosolids sludge together
Separate Dewatering Advantages Uses specific conditioning for WTP residuals No effect on WWTP biosolids dewatering Disadvantages Requires new polymer system and dedicated centrifuges May impact cake disposal options Pilot testing needed to confirm impacts Net decrease likely in % solids in cake Requires dedicated storage for alum sludge
Blended Dewatering Advantages Use existing polymer to condition the two sludges Use existing centrifuges Possible to blend the Croton WTP sludge with Hunts Point sludge prior to dewatering Disadvantages Possibility of lower dewatered cake percent being produced with blended sludge
Effects of Aluminum Hydroxide on Wastewater Limited Research/Literature Therefore, it was decided to pilot test to study the alternatives Full scale using existing Hunts Point WWTP dewatering centrifuges BioWin Computer Modeling used to estimate theoretical effects of introducing WTP residuals to Hunts Point WWTP process
Hunts Point WW Process Concerns BNR Consent Order requiring Total Nitrogen (TN) to under 44,200 lb/d at 2017 influent flows and loads Biowin Analysis included three Croton Residual addition points Primary Settling Tanks Final Settling Tanks Gravity Thickeners
Biowin Model Predictions (1 of 2) Primary Settling (PS) Tanks Increased sludge settling Increased solids can potentially overload Gravity Thickeners & Digesters, and decrease sludge quality from Gravity Thickeners Increases CBOD removal (source of carbon for denitrification process in BNR treatment) 78% increase in PS load, reduces HRT and VSS destruction in digesters, increased methanol demand
Biowin Model Predictions (2 of 2) Final Settling Tanks (FSTs) Addition prior to FST s increased solids loading to clarifiers, lower effective SRT (30% drop) 38% higher solids to digesters, reduced HRT and VSS destruction Gravity Thickeners Potentially higher removal of solids (+37%) No significant drop in PE VSS/TSS ratio, no SRT effects, no increased methanol demand Solids Loading Rates matched WEF MOP Best Alternative of 3 Locations
Previous Bench Scale Tests Results Separate Dewatering Results: WWTP ~ 22 to 27% WTP ~ 18 to 20% Combined Dewatering Results Indicated that dewatered solids from combining sludges ranged between 8 22%
Pilot Study Scope Dewatered alum residuals from Warner WTP at Hunts Point WWTP Warner WTP: similar raw water quality & treatment process to Croton WTP 6,000 gallon truck for residuals 2.5-3% solids Study polymer types and dosage rates that produce high solids cake Polymer for Alum Sludge: Flopam NE1619 Polymer for Wastewater Sludge: Flopam NE1516
WTP Residuals vs. WWTP Biosolids Critical difference that dictates sludge conditioning is Difference in the cationic demand between alum residuals and anaerobically digested biosolids WTP (alum) residuals has a low cationic charge Anaerobically digested biosolids has a high cationic charge Therefore need to study both single (WTP residuals alone) and dual conditioning (combined WTP residuals with WWTP biosolids)
Single & Dual Charge Conditioning Single Conditioning 80% Charge Existing WWTP Polymer, a High Charge Cationic Polymer Dual Conditioning 10% Cationic Charge Polymer 80% Cationic Charge Existing WWTP Polymer
Preliminary Jar Testing Results: Existing Polymer was effective for dewatering the blended sludge Recommended using both types of charged polymers to maximize cake solids Pilot Test: 10% charge polymer into alum feed 80% charge Polymer into WWTP biosolid feed.
Figure 1: Pilot Test Design Imported Sludge Hunt s Point Sludge Feed Centrifuge Alum Sludge Aquarium WTP Alum Feed Pump M Drain Centrate Polymer Tote Existing Polymer Existing Metering Pump Polymer Make Down System Existing Tank Polymer Feed Pump Figure 1: Pilot Test Design Dewatering Dewatered Cake
Figure 2: Pilot Arrangement
Figure 3: Polymer System
Single Conditioning Results (Not Optimized) As alum residuals:biosolids INCREASED Cake solids DECREASED (polymer constant). The lowest cake solids was 22.6% at 4:1 alum to wastewater sludge ratio
Dual Conditioning Results Results at 16-38% alum to wastewater sludge ratios 6:1 blended sludge ratio produced a high cake solids (29%) with 60 lb/dt (neat) Existing Polymer and 45 lb/dt (neat) 10% charge polymer. 4:1 blended sludge ratio, the same cake solids were produced but required 20-30% more polymer 2.5:1 blended sludge ratio, increase in the polymer dosage did not increase the cake solids.
Figure 4: Recommended Operations
Conclusions Dual conditioning produced better cake Maximum Flexibility Allows the flexibility to treat the solids mixture with a proper combination of low and high charge polymers. And..confirmation of existing Hunts Point dewatering equipment will work on Croton WTP residuals, BUT
Direct Sewer Discharge Part Deux NYC DEP Operating Bureau allows Croton Sludge to be pumped to sewer Existing infrastructure has been utilized Sludge monitoring via industrial discharge permit: routine sampling req'd Monitoring of BNR process at WI WWTP shows no impact to treatment Pumping strategy during Wet Weather to mitigate CSO events
Overview of the Facility Location Croton WTP Ward s Island WWTP Hunt s Point WWTP
Questions? Thank you!
Alum Sludge Addition Impacts On Gravity Thickening Need higher GT underflow to digesters Solids Loading Rate does not exceed WEF MOP values (7.1 to 9.5 lb/ft^2/d) On Digestion 5,000-10,000 lb/day additional must be landfilled due to: Under 15-day HRT requirement reducing %VSS destruction Hunt s Point won t meet PSRP compliance for Class B sludge with current online infrastructure May reduce digester performance with decrease in total gas production, Methane production, COD reduction, and organic N decomposition
Alum Sludge Addition Impacts On Dewatering Increase digested sludge load 60-70% Evaluation whether centrifuge capacity exists for additional sludge load necessary Combined sludge produces cake solids of 24% On Biological Nitrogen Removal (BNR) Potential decrease in ammonia production Beneficial reduction of influent N load to secondary treatment May inhibit nitrification which would require supplemental Sodium Hydroxide